This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-081597, filed Mar. 21, 2001, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a liquid crystal display and a display method, particularly, to a liquid crystal display utilizing the combination of a liquid crystal display technology and an electrophoretic display technology and its display method.
2. Description of the Related Art
In the electrophoretic display technology, an image is displayed by utilizing the electrophoretic phenomenon of particles dispersed in a dispersion medium. The dispersion medium containing such particles, i.e., electrophoretic particles, is called an electric field sensitive pigment, i.e., an electrophoretic E-ink or an E-ink. The electrophoretic display technology is classified into two types described below.
In one type of electrophoretic display technology, used is a microcapsule prepared by dispersing charged titania particles 21 in a colored solvent 22 and encapsulating the resultant dispersion with a transparent film 23, as shown in FIG. 1A. In this technology, the displayed color can be switched between the white color of the titania particles and the color of the solvent by applying voltage across the microcapsule to cause the migration of the titania particles 21 within the transparent film 23.
In the other type of electrophoretic display technology, used is a microcapsule prepared by dispersing charged particles 31a and 31b differing from each other in the polarity of the charge and in the color in a transparent solvent 32, and encapsulating the resultant dispersion with a transparent film 33. In the case of using the microcapsule thus prepared, it is possible to switch the displayed color between the color of the charged particle 31a and the color of the charged particle 31b depending on the state that the charged particles 31a are present on the side of the observer and the state that the charged particles 31b are present on the side of the observer.
Incidentally, these technologies are described in, for example, the publications given below:
[1] B. Comiskey, J. D. Albert and J. Jacobson, Digest of SID97, p75;
[2] P. Drzaic, B. Comiskey, J. D. Albert, L. Zhang, A. Loxley and R. Feeney, Digest of SID98, p1131; and
[3] Barrett Comiskey, J. D. Albert, Hidekazu Yoshizawa and Joseph Jacobson, Nature, 394, p253 (1998).
The electrophoretic display technology permits obtaining a high contrast. However, it is difficult to provide a full color image. To be more specific, in the display technology using the microcapsule shown in FIG. 1A, the displayed color is switched between two colors, i.e., the white color produced by the light-scattering by the titania particles 21 and the color of the colored solvent 22, with the result that a color filter is required for producing a full color image. In the display technology using the microcapsule shown in FIG. 1B, the displayed color is also switched between two colors, i.e., the color of the electrophoretic fine particles 31a and the color of the electrophoretic fine particles 31b, with the result that it is also necessary to use a color filter for producing a full color image. In the case of using a color filter, however, the light utilization efficiency is lowered so as to lower the contrast.
In order to produce a full color image by the electrophoretic display technology, proposed is a method of coloring appropriately the electrophoretic particles. According to this coloring method, it is unnecessary to use a color filter. However, the reflectance is lowered in the case of displaying a white image. Also, the reflectance is increased in the case of displaying a black image. It follows that the image quality is lowered.
In order to realize a full color display while maintaining a high contrast, it is absolutely necessary to switch the displayed color among three colors of white, black and a color other than white and black in a single microcapsule. However, such a technology has not yet been developed to date.
In order to overcome the problem pointed out above, the present inventors have proposed an electrophoretic display technology that permits switching the displayed color among three colors in a single microcapsule. In the display technology proposed by the present inventors, used is a microcapsule prepared by dispersing fine particles such as titania particles in a P-type liquid crystal material containing a liquid crystal substance, a dichroic dye and an isotropic dye, and encapsulating the resultant dispersion with a transparent film. Where the dichroic dye contained in the microcapsule can exhibit a complementary color of the isotropic dye, it is possible to switch the displayed color among three colors of white, black and a color other than white and black in a single capsule. It follows that the electrophoretic display technology proposed by the present inventors makes it possible to achieve a full color display while maintaining a high contrast characterizing the display of electrophoresis mode.
It is expected to apply the electrophoretic display to an electronic paper. In such an application, it is required to decrease the power consumption of the display. Therefore, it is desirable for the electrophoretic display to be capable of holding the image displayed by the voltage application even after stopping the application of voltage. In other words, it is desirable for the electrophoretic display to exhibit a memory function.
The display noted above certainly exhibit the memory function in the case where an image is displayed by the electrophoresis mode. However, the memory function is not exhibited in the case where an image is displayed by the guest-host mode. To be more specific, it is certainly possible to hold white and black colors even after stopping the application of voltage. However, it is impossible to hold the color other than white and black. Such being the situation, a clear full color image, which is displayed under the state that voltage is applied, is switched into a monochromatic image immediately after stopping the application of voltage.
According to a first aspect of the present invention, there is provided a liquid crystal display, comprising a substrate and pixels arrayed on the substrate, each of the pixels comprising an electric field sensitive layer which comprises an N-type liquid crystal material containing a liquid crystal substance, a dichroic dye and an isotropic dye, and particles dispersed in the N-type liquid crystal material and configured to migrate in the N-type liquid crystal material by electrophoresis.
According to a second aspect of the present invention, there is provided a liquid crystal display, comprising a substrate and pixels arrayed on the substrate, each of the pixels comprising a first electric field sensitive layer which comprises an N-type liquid crystal material containing a first liquid crystal substance, a first dichroic dye and a first isotropic dye, and first particles dispersed in the N-type liquid crystal material and configured to migrate in the N-type liquid crystal material by electrophoresis, and a second electric field sensitive layer which is adjacent to the first electric field sensitive layer and comprises a P-type liquid crystal material containing a second liquid crystal substance, a second dichroic dye and a second isotropic dye, and second particles dispersed in the P-type liquid crystal material and configured to migrate in the P-type liquid crystal material by electrophoresis.
According to a third aspect of the present invention, there is provided a method of displaying an image, comprising changing a state of a first electric field sensitive layer among first to third states, the first electric field sensitive layer comprising an N-type liquid crystal material which contains a first liquid crystal substance, a first dichroic dye and a first isotropic dye, and first particles dispersed in the N-type liquid crystal material and configured to migrate in the N-type liquid crystal material by electrophoresis, wherein the first state is a state that the first particles are gathered in an observer side region of the first electric field sensitive layer, the second state is a state that the first particles are gathered in a back side region of the first electric field sensitive layer which is apart from the observer side region of the first electric field sensitive layer and an alternating-current voltage is applied to the first electric field sensitive layer, and the third state is a state that the first particles are gathered in the back side region of the first electric field sensitive layer and no voltage is applied to the first electric field sensitive layer.
The term xe2x80x9cdichroic dyexe2x80x9d represents a dye having a dichroic ratio larger than 1.5, and the term xe2x80x9cisotropic dyexe2x80x9d represents a dye or pigment having a dichroic ratio equal to or smaller than 1.5. The term xe2x80x9cN-type liquid crystal materialxe2x80x9d represents a liquid crystal material having a negative dielectric anisotropy, and the term xe2x80x9cP-type liquid crystal materialxe2x80x9d represents a liquid crystal material having a positive dielectric anisotropy. Further, the term xe2x80x9cobserver side regionxe2x80x9d represents a region facing the observer, and the term xe2x80x9cback side regionxe2x80x9d represents a region remote from the observer, compared with the xe2x80x9cobserver side regionxe2x80x9d.
It is possible for the method according to the third aspect of the present invention to further comprise changing the state of a second electric field sensitive region among fourth to sixth states. In this case, it is possible for the second electric field sensitive layer to comprise a P-type liquid crystal material containing a second liquid crystal substance, a second dichroic dye and a second isotropic dye, and second particles dispersed in the P-type liquid crystal material and configured to migrate in the P-type liquid crystal material by electrophoresis. It is possible for the fourth state to be a state that the second particles are gathered in a observer side region of the second electric field sensitive layer. It is possible for the fifth state to be a state that the second particles are gathered in a back side region of the second electric field sensitive layer and an AC voltage is applied to the second electric field sensitive layer. Further, it is possible for the sixth state to be a state that the second particles are gathered in the back side region of the second electric field sensitive layer and no voltage is applied to the second electric field sensitive layer.
It is possible for the display according to the first aspect of the present invention to further comprise a transparent film encapsulating an N-type liquid crystal material and particles so as to form a microcapsule. Likewise, in each of the second and third aspects of the present invention, it is possible for the first electric field sensitive layer to further comprise a first transparent film encapsulating an N-type liquid crystal material and first particles so as to form a first microcapsule. Further, in each of the second and third aspects of the present invention, it is possible for the second electric field sensitive layer to further comprise a second transparent film encapsulating a P-type liquid crystal material and second particles so as to form a second microcapsule.
In the first aspect of the present invention, it is possible for a dichroic ratio of the dichroic dye to be 3 or more. Likewise, in each of the second and third aspects of the present invention, it is possible for a dichroic ratio of the first dichroic dye to be 3 or more and for a dichroic ratio of the second dichroic dye to be 3 or more.
In the first aspect of the present invention, it is possible for the dichroic dye to exhibit a complementary color of the isotropic dye. Likewise, in each of the second and third aspects of the present invention, it is possible for the first dichroic dye to exhibit a complementary color of the first isotropic dye and for the second dichroic dye to exhibit a complementary color of the second isotropic dye. Also, in the third aspect of the present invention, it is possible for the color of the first electric field sensitive layer under the second state to be equal to the color of the second electric field sensitive layer under the sixth state and for the color of the first electric field sensitive layer under the third state to be equal to the color of the second electric field sensitive layer under the fifth state.
In each of the first and second aspects of the present invention, it is possible for each of the pixels to be configured to exhibit white, black and a color other than white and black.
In the first aspect of the present invention, it is possible for the particles to have a mean diameter equal to or less than 0.4 xcexcm. Similarly, in each of the second and third aspects of the present invention, it is possible for the first particles to have a mean diameter equal to or less than 0.4 xcexcm and for the second particles to have a mean diameter equal to or less than 0.4 xcexcm.
In the second aspect of the present invention, it is possible for each of the pixels to further comprise a pixel electrode. It is possible for the pixel electrode to comprise, for example, a first sub-pixel electrode between the substrate and the first electric field sensitive layer and a second sub-pixel electrode between the substrate and the second electric field sensitive layer. In this case, it is possible for each of the pixels to further comprise a first switching element electrically connected to the first sub-pixel electrode and a second switching element connected to the second sub-pixel electrode. Also, it is possible for each of the pixels to further comprise a counter electrode facing the pixel electrode such that the first and second electric field sensitive layers sandwiched between the pixel electrode and the counter electrode.
Further, in the second aspect of the present invention, it is possible for the pixels to comprise a first pixel in which each of the first dichroic dye and the first isotropic dye can exhibit a cyan color, and each of the second dichroic dye and the second isotropic dye can exhibit a red color, a second pixel in which each of the first dichroic dye and the first isotropic dye can exhibit a magenta color and each of the second dichroic dye and the second isotropic dye can exhibit a green color, and a third pixel in which each of the first dichroic dye and the first isotropic dye can exhibit a yellow color and each of the second dichroic dye and the second isotropic dye can exhibit a blue color.